Analyzers used to test body liquids for their concentration of analytes often use slide-like test elements. A small amount of a patient sample liquid is dispensed from a pipette onto such a test element, which is then incubated and "read" for a detectable change indicative of the concentration of analyte. Frequently, "n" dispensing steps occur from the same patient sample, onto "n" different test elements to run "n" different assays. This requires each sample at the pipette to remain at the dispensing station until all the "n" dispensing events are made. (The sample is usually contained in a disposable tip in the pipette.)
In high speed analyzers, little delay occurs between each of those "n" dispensing events. However, in some newer analyzers, delays as much as 3.5 minutes can occur between sequential dispensing. An example includes those analyzers that have the detecting or "read" station located off the incubator, and which test for rate assays as well as end-point assays. Such rate assays require a single test element to remain at the detecting station for one minute or more, while as many as 95 separate readings are taken to confirm the rate of change of the signal. This means that the incubator upstream is unable to offload any other test elements. This in turn prevents new test elements from having sample liquid dispensed thereon, since there is no room in the incubator to place them. Thus, the pipette has to delay substantially, with exposed sample in the tip, until the next amount of sample can be dispensed.
A delay between sequential dispensing by the pipette is particularly significant if the patient sample has high amounts of protein, as is often the case. Without a cover placed over the exposed dispensing tip, such sample can dry up, plugging the tip to prevent the next dispensing step. Alternatively, the analyte concentration can be unacceptably altered due to sample evaporation at the tip.
Pipette tips have been covered in the past to prevent this problem. However, such constructions have involved either operator-handling of the covers (to remove them and replace them), or separate analyzer actuation in response to the operator or a signal indirectly responsive to a new test element entering the system. Separate operator intervention is undesirable as it is a source of errors and delays. Any automated operation of tip covers that is only indirect, is also subject to delays and errors due to separate action required by the analyzer.
What has been needed, prior to this invention, particularly in analyzers having significant delays between sequential dispensing of patient sample, is capping means for the pipette tips that are directly operated, that is, removed, by the presence of a test element ready for dispensing. In this way, the tip uncovering is only responsive to the direct presence of the test element to be spotted, and there is avoided the chance of error that is possible with less direct actuation or removal of the capping means.